The drive device serves, for example, to drive a motor vehicle and in this respect, therefore, to supply a torque directed at driving the motor vehicle. The drive device is equipped with a plurality of drive assemblies, namely, a first drive assembly designed as an internal combustion engine and a second drive assembly designed as an electric motor. The drive device is accordingly a hybrid drive device. The drive device is equipped, for example, with an output shaft, which can be coupled to the internal combustion engine and to the electric motor.
For example, the internal combustion engine and/or the electric motor can be coupled to the output shaft via a gearshift transmission. For this purpose, the motor shaft of the electric motor is linked, for example, to a transmission input shaft of the gearshift transmission, preferably rigidly and/or permanently. In contrast, a transmission output shaft of the gearshift transmission can be coupled to the driven shaft, preferably rigidly and/or permanently. However, it can also be provided that another clutch, in particular another shift clutch, is provided between the transmission output shaft and the driven shaft.
The electric motor can be coupled to the internal combustion engine via the shift clutch. The internal combustion engine can hereby be decoupled, preferably at the same time, both from the electric motor and from the driven shaft by opening or disengaging the shift clutch. The shift clutch has a plurality of shifting states, wherein, in a first shifting state of the shift clutch, the internal combustion engine or its drive shaft is decoupled from the electric motor or the motor shaft of the electric motor and, in a second shifting state, is coupled to it. In the second shifting state, a slip-free connection between the internal combustion engine and the electric motor or between the drive shaft and the motor shaft is produced, that is, without clutch slippage of the shift clutch.
For startup of the internal combustion engine, it is usually necessary to drag it, in particular, until the internal combustion engine has attained a specific speed. This specific speed can be, for example, a minimum speed or an idling speed of the internal combustion engine. The minimum speed is understood to mean the speed of the internal combustion engine at which it is able to increase its speed further automatically, that is, without the influence of an external torque and, in particular, therefore, in the case of a fully disengaged shift clutch, preferably toward the idling speed. In contrast, the idling speed is a speed to which the internal combustion engine is adjusted when it is not used for driving the motor vehicle or, more generally, for supplying a torque. The idling speed is usually greater than the minimum speed.
The dragging of the internal combustion engine occurs through at least partial closing or engaging of the shift clutch, that is, through the adjustment of a desired clutch torque at the shift clutch. The desired clutch torque is thereby different from zero and, in particular, is greater than zero. An actual clutch torque that is transmitted from the motor shaft to the drive shaft by means of the shift clutch is adjusted to the desired clutch torque, for example in a controlling manner and/or regulating manner. Correspondingly, a torque corresponding to the desired clutch torque is applied to the internal combustion engine, so that its speed increases. The desired clutch torque used for startup of the internal combustion engine is adjusted at the shift clutch over the dragging period. Preferably, the desired clutch torque is kept constant over the dragging period. At the end of the dragging period, the shift clutch is preferably completely disengaged in order to enable an automatic acceleration of the internal combustion engine. In this regard, the dragging period defines the period of time throughout which the speed of the internal combustion engine is increased by means of the torque transmitted via the shift clutch, whereby, at the end of the dragging period, the internal combustion engine preferably has the minimum speed or the idling speed and, in particular, has exactly said speed.
The desired clutch torque is usually chosen in such a way that clutch slippage arises at the shift clutch, that is, such that the speed of the drive shaft is different from the speed of the motor shaft. Depending each time on the design of the shift clutch, a specific quantity of heat hereby accrues. In particular, when the shift clutch is designed as a dry shift clutch, that is, as a shift clutch without direct cooling by a coolant, this quantity of heat is of particular importance, because it can influence the behavior of the shift clutch.